Intraluminal prostheses used to maintain, open, or dilate blood vessels are commonly known as stents. Stent constructions generally include lattice type cylindrical frames that define a plurality of openings. Stents may have self-expanding and/or balloon expandable properties. Stents can be made of various metals and polymers and can include a combination of self-expanding and balloon expandable properties.
Synthetic vascular grafts are routinely used to restore the blood flow in patients suffering from vascular diseases. For example, prosthetic grafts made from expanded polytetrafluoroethylene (ePTFE) are commonly used and have shown favorable patency rates, meaning that depending on a given time period, the graft maintains an open lumen for the flow of blood therethrough. Grafts formed of ePTFE include a microstructure characterized by spaced apart nodes connected by fibrils, the distance between the nodes defined as internodal distance (IND), and are generally extruded either as a tube or as a sheet or film that is fashioned into a tube.
It is known in the art to use stents in combination with vascular grafts or covering layers to form stent-grafts. A vascular graft or covering layer, such as an ePTFE tube, is positioned adjacent an inner and/or outer surface of the stent and adhered thereto. For instance, U.S. Pat. No. 6,004,348 to Banas et al., which is incorporated by reference in its entirety into this application, describes an encapsulated stent formed by providing a first ePTFE graft about a mandrel, concentrically positioning a stent about the first ePTFE graft, and concentrically positioning a second ePTFE graft about the stent. Circumferential pressure is then applied to the assembly by helically wrapping ePTFE tape under tension over the outer surface of the second ePTFE graft. Thereafter, the assembly is heated to bond the first ePTFE graft to the second ePTFE graft through the openings of the stent. Following the sintering process, the ePTFE tape is unwrapped from the assembly.
U.S. Pat. No. 6,214,039 to Banas et al. describes a method of forming a stent-graft with a single graft or covering layer disposed on the abluminal surface of the stent, including sliding an ePTFE graft over a tapered mandrel with an increasing diameter to dilate the ePTFE graft and then sliding the dilated graft onto an unexpanded stent such that the graft is retained about an outer surface of the stent by the inherent recoil properties of the graft. Methods of forming a stent-graft with a single graft or covering layer on the luminal surface of the stent generally involves the use of adhesives or coatings positioned on the stent and/or surface of the graft. For example, an ePTFE graft is placed on a mandrel and a stent with a polymeric coating is positioned over the graft. As with the encapsulation procedure described above, tape is then helically wrapped about the outer surface of the stent under tension and the stent-graft is heated to achieve bonding of the ePTFE graft to the coated stent. However, differently from the encapsulation procedure, removal of the tape from the stent-graft is often difficult due to the tendency of the stent coating to melt and bond to the tape, such that the removal process may result in tearing of the graft and/or deposit of tape fragments on the stent-graft (requiring manual removal).
It is advantageous to have a graft or covering layer on the luminal surface of the stent-graft in order to provide a smooth surface for the flow of blood through the stent-graft. Moreover, a stent-graft with a single luminal graft or covering layer may provide advantages over a stent-graft with two or more graft layers, such as providing a lower profile for insertion and increasing flexibility. Thus, a method of applying pressure to the stent-graft with a single luminal graft or covering layer is desirable.
References related to stent-grafts include: U.S. Pat. Nos. 6,004,348; 6,214,039; 6,364,903; 6,488,701; and U.S. Patent Application Publication No. 2005/0096737, each of which is incorporated by reference in its entirety into this application.
Applicants have recognized that it would be desirable to provide a method for forming a stent-graft with a single graft layer on the luminal surface of the stent, embodiments of which are described herein.